1. Field of the Invention
The present invention relates to an anti-theft device of an automobile for protecting the automobile from being stolen or from being intruded.
2. Prior Art
Various anti-theft devices for an automobile have been proposed. A first example is shown in Published Unexamined Japanese Utility Model Application No. Sho-58-86775 in which an anti-theft device operates on an independent exclusive battery prepared besides an ordinary main battery for the automobile. The anti-theft device remains powered and will work even if a cable from the main battery is cut from outside of the automobile through the front grill.
A second example is shown in Published Unexamined Japanese Patent Application No. Sho-58-35694 in which a memory circuit stores a locked state of the automobile and an alarm buzzer is activated when a door is opened by false measures despite the memorized locked state.
A third example is shown in Published Unexamined Japanese Patent Application No. Sho-59-45246 in which an alarm controller is connected to a memory circuit. An output data from the alarm controller is stored in the memory circuit so that a theft by a battery disconnection or after a battery has worn-out can be prevented.
Those are devices for alarming or preventing a false access to an automobile. Another type of anti-theft devices requires an identification of a driver to release a once locked condition and to start the engine. One such type is a device, a fourth example with a radio emitter. A driver holding the radio emitter can open the door since a receiver mounted on the automobile recognizes a special radio signal from the emitter.
Another example, a fifth example, of such type uses a special ignition key in which an electrical resistance of a particular resistance value is embedded. The resistance value of the inserted key is measured by the device to check whether it is an authentic key.